This invention relates to a screening test for cancerous and precancerous conditions of the large intestine and other body sites and to a kit containing the components necessary for conducting the test.
Cancer is a major public health problem in the world. Even as pharmaceutical agents for the treatment of cancer are developed, early detection and prevention are still the best hope for combating this human tragedy. Shamsuddin et al., Human Pathology 19:7-10, 1988, has recently developed a screening test for colorectal cancer which can detect cancer of the large intestine employing rectal mucus. The mucus is reacted with the enzyme galactose oxidase by moistening a cellulose membrane filter, which had previously been impregnated with a phosphate buffer solution of the enzyme and then lyophilized, and then contacting the moistened cellulose membrane filter with a Metricel membrane filter bearing the mucus sample for 1-2 hours. The mucus bearing membrane filter is then washed with distilled water for 1 minute, reacted with basic fuchsin for 15 minutes, washed in tap water for 10 minutes and then air dried. This procedure, although simple, is lengthy. It also suffers from the serious deficiency that, if a patient tests negative by the screening test, it can mean either a biological negative, i.e., the patient does not have a cancerous or precancerous condition which releases a marker carbohydrate employed in the screening test, or it is technically negative, i.e., and insufficient mucus from the rectum was obtained in order to detect any marker carbohydrate present therein. The latter situation could mean a "false negative", the consequence of which could be dangerous to the person tested since any cancer present could continue to grow undetected because the negative results would give the patient a false sense of security which might cause the patient or his/her physician to disregard symptoms that might otherwise be investigated if the negative results had not been obtained.
Another deficiency of the prior art test is the unstable nature of the basic fuchsin employed is a critical component therein. According to the prior art, basic fuchsin must be prepared fresh and discarded after a week because of its instability. (Manual of Histological Staining Methods of the Armed Forces Institute of Pathology, Ed. 3, McGraw-Hill, New York 1968, p. 159.) This makes it impossible to provide the materials required to conduct the screening test in kit form, since shipping, handling and storage of such kits would require a shelf life of at least six months and the instability of the basic fuchsin would preclude such a shelf life.
Finally, as noted above, the prior art screening test, in addition to several hours of preparation for lyophilization of galactose oxidase, requires more than two hours to obtain the results thereof, which makes the test impractical for mass screening of large segments of the population.
Since most cancers in humans are believed to be the result of exposure to one or more environmental carcinogens which are excreted through the large intestine or urinary bladder, it can be expected that the carcinogen(s) and/or their metabolite(s) cause changes in those organs. Based on this hypothesis or threat of the presence of a cancerous or precancerous condition in the body of an individual, including but not restricted to the large intestine, can be detected accurately by the method of this invention using rectal sampling, without the prior risk of false negatives which limited the value of this technique as a screening test for the general population. The present invention eliminates false negative results which are obtained as a result of inadequate sampling, permits rapid testing for the presence or absence of precancer or cancer carbohydrate markers in less than 15 minutes and ensures the stability of the critical components required to conduct the test for over one year.